Common brassiere steel rings are usually made of metal materials and have two types of cross section, i.e., round and flat. Given a certain material property and overall shape of a steel ring, its force resistance property and anti-fatigue ability are determined. Therefore, many designers focus their directions mainly on the shape and material of the steel ring. However, they have not made significant improvements to the shape of the cross section of the steel ring.
It has been verified by scientific experiments that a steel ring made of a steel wire having a round cross section has relatively high anti-fatigue ability when being stretched or compressed. However, due to its round cross section, the forces applied on it are isotropic, i.e., the forces from all directions have no difference, while when being worn, the forces applied on the steel ring, mainly the stretching force and the compressing force, are asymmetric. Therefore, a steel ring having a round cross section results in either a waste in materials or an insufficiently applied force in the stretching direction or compressing direction.
Therefore, a steel ring having a flat cross section, i.e., a steel ring formed by pressing a steel wire into a flat shape is mostly used in prior art. Although a steel ring having a flat cross section has smaller longitudinal resistance, i.e., smaller supporting strength compared to a steel ring having a round cross section, and therefore is easy to deform, it provides another advantage, i.e., more comfortable wearing experience. However, on the other hand, it has poor anti-fatigue ability and therefore has a short life.
Many improvements to the shape of the steel ring have been developed in prior art. However, none of them can solve this problem: on one hand, a steel ring that is easy to be stretched is thus easy to be bent inwardly and deformed, resulting in a short life; on the other hand, a steel ring that is hard to be stretched is thus hard to be bent inwardly, resulting in a long time to fit to a user's body and making the user feel uncomfortable for a long time.
Therefore it is a common practice in the art to improve the life of a steel ring by enlarging the area of its cross section. However, the inventor of the present application found by fatigue resistance experiments that given a specific design of the cross section, the steel ring's fatigue resistance will start to decrease when the area of the cross section increases to a certain value. After analysis, the inventor found that this is due to interactions between molecules in the inner and outer edges of the steel ring when a force is applying on it. This interaction increases as the area of its cross section increases, and is easy to make the overall steel ring to reach its fatigue limit. Therefore, it is wrong to just simply increase the area of the cross section of a steel ring, which is a bias in the prior art that no one else have ever found.